1. Introduction
The variations of pressure and temperature that characterize a metamorphic event are a function
of the tectonic setting and of the processes that were active during metamorphism England and
Thompson, 1984; Thompson and England, 1984; Bohlen, 1987; Harley, 1989; Brown, 1993. Thus,
the thermal evolution of a metamorphic belt has been regarded as one of the most important keys
to understanding the tectonic history of complex metamorphic terranes, and metamorphic P – T
paths have been used successfully to constrain the tectonic setting and processes Harley, 1985, 1988;
Mezger et al., 1990; Bohlen, 1991; Mengel and Rivers, 1991. Generally, clockwise, especially
isothermal decompressional, P – T paths are con- sidered to develop in continental collisional envi-
ronments
England and
Thompson, 1984;
Thompson and England, 1984; Bohlen, 1991; Brown, 1993, whereas anticlockwise, especially
isobaric cooling, P – T paths are interpreted to be related to the intrusion and underplating of
mantle-derived magma which may occur in intra- continental magmatic arc regions Wells, 1980;
Bohlen, 1987, 1991, hot spots related to mantle plumes Bohlen, 1991 and incipient rift environ-
ments Sandiford and Powell, 1986. However, inferences about tectonic setting and process
based on P – T paths are often complicated by variations in P – T data from different rock units
or tectonic domains within the same terrane Selverstone and Chamberlain, 1990. For exam-
ple, contrasting P – T paths have been observed between anticlines and adjacent synclines, or be-
tween hanging and foot wall of the same fault Chamberlain and Karabinos, 1987.
As one of the best exposed Archean to Pale- oproterozoic cratonic blocks in the world, the
North China Craton is a promising area for ap- plying the large-scale synthesis approach of meta-
morphic P – T paths to understanding tectonic settings and processes, since numerous studies on
the tectonothermal evolution of basement rocks have been undertaken throughout the craton in
the past decade and a P – T data base, largely published in Chinese, is now available Cui et al.,
1991; Jin et al., 1991; Lu, 1991; Li, 1993; Liu et al., 1993; Lu and Jin, 1993; Sun et al., 1993a;
Chen et al., 1994; Ge et al., 1994; Zhao et al., 1998, 1999a. Zhao et al. 1998, 1999a have sum-
marized the P – T paths of basement rocks in the eastern and western parts of the craton and dis-
cussed their tectonic implications. On the basis of lithological,
structural, metamorphic
and geochronological data, Zhao et al. 1998, 1999a
proposed that the North China Craton may have been composed of two separate continental
blocks, called the Eastern and Western Blocks, from the late Archean to Paleoproterozoic and
the 1.8 Ga collision between these two blocks along the Central Zone resulted in the final amal-
gamation of the North China Craton Wu et al., 1991; Wu and Zhong, 1998; Zhao et al., 1998,
1999a. The purpose in this communication is to examine the collision-related tectonothermal evo-
lution of various rock units and metamorphic domains in the Central Zone and, in combination
with lithological, structural and geochronological data to further constrain the Paleoproterozoic
amalgamation of the Eastern and Western Blocks which formed the North China Craton.
2. Regional setting
The North China Craton is the largest and oldest known cratonic block in China, covering
an area of more than 1 500 000 km
2
, and is bounded by faults and younger orogenic belts
Fig. 1. The early Paleozoic Qilianshan QLS Orogen and the late Paleozoic Tianshan – Inner
Mongolia – Daxinganling TIMD Orogen bound the craton to the west and the north, respectively,
whereas in the south the Mesozoic Qinling – Da- bie – Su – Lu QDSL high- to ultrahigh-pressure
belt separates the craton from the South China Craton Fig. 1.
The tectonic evolution of the North China Cra- ton is poorly constrained. Traditionally, it has
been considered to be composed of a uniform Archean crystalline basement, overlain by a
Proterozoic to Cainozoic cover, and its history was explained using a pre-plate tectonic geosyn-
clinal-style model Huang, 1977. Terrane accre- tion and collisional models have only been
applied recently Li et al., 1990; Zhai et al., 1992; Wang et al., 1996; Zhao et al., 1999a,b, including
recognition of a Paleoproterozoic orogen along the central North China Craton, named the Cen-
tral Zone, which separates the craton into West- ern and Eastern Blocks Fig. 2; Zhao et al.,
1999a,c.
The Eastern
Block includes
the Miyun –
Chengde, Eastern
Hebei, Western
Liaoning, Western Shangdong, Eastern Shandong, Southern
Liaoning, Northern Liaoning and Southern Jilin domains Fig. 2. It consists predominantly of
Late Archean domiform tonalitic – trondhjemitic – granodioritic TTG batholiths and − 2.5 Ga syn-
tectonic
granites outlined
by anastomosing
networks and linear belts of open to tight syn- forms of minor volcanic and sedimentary rocks
metamorphosed in greenschist to granulite facies at 2.5 Ga, with anticlockwise P – T paths Cui
et al., 1991; Li, 1993; Ge et al., 1994; Sun et al., 1993b; Song et al., 1996; Kro¨ner et al., 1998;
Zhao et al., 1998. Some Early to Middle Archean rocks are locally present in the Eastern Block
Huang et al., 1986; Jahn et al., 1987; Qiao et al., 1987; Liu et al., 1992; Song et al., 1996, but their
tectonic nature and deformational and metamor- phic history are unclear due to reworking during
the 2.5 Ga tectonothermal event. The Western Block,
including the
Helanshan – Qianlishan, Daqingshan – Ulashan,
Guyang – Wuchuan, Sheerteng and Jining domains Fig. 2, has a late
Archean lithological assemblage, structural style and metamorphic history similar to that of the
Eastern Block Li et al., 1987; Shen et al., 1987, 1990; Jin et al., 1991; Liu et al., 1993; Lu and Jin,
1993, but differs by the absence of Early to Middle Archean assemblages and by being over-
lain by and interleaved with Paleoproterozoic khondalites. The latter, defined as a suite of gran-
ulite facies supracrustal rocks including graphite- bearing sillimanite-garnet gneisses and associated
garnet-bearing
felsic paragneisses
leptynites, quartzites, calc-silicate rocks and marbles, were
affected by a 1.8 Ga metamorphic event char-
Fig. 1. Outline tectonic map of China showing the major Precambrian blocks and the Late Neoproterozoic and Paleozoic: fold belts. HY, Himalaya fold belt; KL, Kunlun fold belt; QDSL, Qinling – Dabie – Su – Lu fold belt; QLS, Qilianshan fold belt; TIMD,
Tianshan – Inner Mongolia – Daxinganling fold belt.
Fig. 2. Distribution of the basement rocks in the North China Craton and the distribution of the Eastern and Western Blocks and the Central Zone Inset. The Eastern Block includes the Anshan – Benxi AB, Eastern Hebei EH, Eastern Shandong ES,
Myun – Chengde MC, Northern Liaoning NL, Southern Jilin SJ, Southern Liaoning SL, Western Liaoning WL and Western Shandong WS domains; Western Block includes the Daqingshan – Ulashan DU, Guyang – Wuchuan GW, Helanshan – Qianlis-
han HQ, Jinning JN and Sheerteng ST domains; and the Central Zone includes the Dengfeng DF, Fuping FP, Hengshan HS, High-Pressure Granulite HPG, Huaian HA, Lu¨liang LL, Northern Hebei NH, Taihua TH, Wutai WT, Zanhuang
ZH and Zhongtiao ZT domains. HLDD, Huashan – Lishi – Datong – Duolun Fault; XKSJ, Xinyang – Kaifeng – Shijiazhuang – Jian- ping Fault.
acterized by clockwise P – T paths Jin et al., 1991; Lu, 1991; Liu et al., 1993; Lu and Jin, 1993; Zhao
et al., 1999a. Separating the two blocks is the Central Zone
which extends as a north – south trending belt across the North China Craton Fig. 2. The zone
consists of a series of greenschist- to granulite-facies metamorphic
terrains containing
re-worked Archean components derived from the Western
and Eastern Blocks, together with late Archean to Paleoproterozoic juvenile igneous and sedimentary
rocks. Geochemical studies of metamorphosed mafic rocks suggest that the basement rocks in the
Central Zone developed in continental magmatic are and intra-arc basin environments Bai, 1986;
Geng and Wu, 1990; Wu et al., 1991; Zhang et al., 1991; Bai et al., 1992; Wang et al., 1996 and were
metamorphosed in greenschist to granulite facies at about 1.9 – 1.8 Ga Wilde et al., 1997, 1998; Wu et
al., 1997; Zhao et al., 1999b; Zhao et al., in press. These arcs and intra-arc basins most likely devel-
oped on the western margin of the Eastern Block, since most reworked mid-Archean TTG gneisses
and granulites discovered in the Central Zone show compositional features and isotopic ages similar to
those in the Eastern Block Zhao et al., 1999c.
The Central Zone is separated from the West- ern Block by the Huashan-Lishi-Datong-Duolun
HLDD Fault and from the Eastern Block by the Xingyang-Kaifeng-Shijiazhuang-Jiianping XKSJ
Fault Fig. 2. Both faults strike N – S in the central and southern parts and turn to N – E in
the north Fig. 2. The central and southern seg- ments of the XKSJ Fault are also called the
Zhuoxian-Shijiazhuang
Fault and
Xingtai- Anyang Fault and constitute part of a major fault
system in the eastern part of China Ren, 1980. The
presence of
voluminous mantle-derived
basalts exposed along the two faults suggests that these faults are deep-seated, possibly reaching into
the lower crust or upper mantle Ren, 1980. Geophysical data indicate a westward increase of
depth to the Moho across the Central Zone from 37 km in the east along the XKSJ Fault to 42 km
in the west along the HLDD Fault Ren, 1980. The exact ages of these two faults have not been
determined, but a major phase of activity was presumably in the Mesozoic, as shown by the
eruption of voluminous basalts along the faults Ren, 1980. Therefore, whether these two faults
represent the original fundamental boundaries be- tween the two blocks and the Central Zone re-
mains unknown. The interpretation preferred here is that the two faults represent cryptic Late
Archean to Paleoproterozoic tectonic boundaries that were reactivated during the Mesozoic.
3. Basement rocks in the Central Zone and their radiometric ages
Kategori